If it was the same NPC, then you never defeated him/her. If you just submit, and boost away, you haven't defeated them. An NPC can jump into super cruise just as fast as you can. This leaves them free to interdict you again, and again.
To really get rid of them you have to either win the interdiction mini-game, leaving them in regular space, with the long FSD cooldown. Or, destroy your attacker's ship through combat.
To really get rid of them you have to either win the interdiction mini-game, leaving them in regular space, with the long FSD cooldown. Or, destroy your attacker's ship through combat.